Fix: highlight sidebar's active section (#2366)

* - fix: highlight active sidebar section / link
- fix: caching crd definitions to prevent sidebar's scroll jumps
- refactored & simplified `Sidebar` and `SidebarItem`

Signed-off-by: Roman <ixrock@gmail.com>

* responding to comments

Signed-off-by: Roman <ixrock@gmail.com>

* adding @jsdoc comments to SidebarItem

Signed-off-by: Roman <ixrock@gmail.com>

src/renderer/components/+custom-resources/custom-resources.tsx

@@ -2,7 +2,7 @@ import React from "react";
 import { observer } from "mobx-react";
 import { Redirect, Route, Switch } from "react-router";
 import { TabLayout, TabLayoutRoute } from "../layout/tab-layout";
-import { crdResourcesRoute, crdRoute, crdURL, crdDefinitionsRoute } from "./crd.route";
+import { crdDefinitionsRoute, crdResourcesRoute, crdURL } from "./crd.route";
 import { CrdList } from "./crd-list";
 import { CrdResources } from "./crd-resources";
 
@@ -14,7 +14,7 @@ export class CustomResources extends React.Component {
         title: "Definitions",
         component: CustomResources,
         url: crdURL(),
-        routePath: crdRoute.path.toString(),
+        routePath: String(crdDefinitionsRoute.path),
       }
     ];
   }